Although, IL-2 was discovered more than three decades ago, novel functions of this pleiotropic cytokine are still being discovered (1). These include the role of IL-2 in maintenance of immune tolerance and regulation of T-helper cell (Th) function for organ-specificity of inflammation (14-18). The current invention pertains to the utilization of IL-2 in conjunction with a recently described cytokine IL-33.
Regulatory T-Cells and IL-2:
The Foxp3+CD4+ Regulatory T-cells (Treg) are important for peripheral tolerance and the deficiency of Treg cells has been demonstrated to be an underlying factor for several autoimmune and inflammatory diseases (3-5). The differentiation, survival and the function of the Treg cells is critically dependent on Interleukin-2 (IL-2) (19-22). Mice that are deficient in IL-2 have reduced proportions and numbers of Treg cells. Consequently, there is uncontrolled activation of immune cells leading to a lymphoproliferative disorder, multi-organ inflammation and death between 1 to 4 months of life compared to the normal mice (14-16, 18).
IL2 and Th2 Cells:
IL-2 is produced by the immune cells (mainly T-cells) and supports the homeostasis and function of another important cell-type of the immune system known as Th2 cells. IL-2 regulates the development and function of the Th2 cells in vivo (14, 16). The primary function of the Th2 cells is to fight parasitic infections and boost the production of anti-parasitic antibodies by the B-cells. However, they have also been known to suppress organ-specific inflammation during autoimmunity, observed in type 1 diabetes (T1D; also referred to as diabetes mellitus type 1) and multiple sclerosis (MS) (23-26). The Th2 cells have also been recognized as potent suppressors of Th1 cells and cytolytic T-cells that induce organ rejection during transplantation (27-31).
Treg Independent Anti-Inflammatory Functions of IL-2:
IL-2 has been shown to be important negative regulator of inflammation via regulating Treg homeostasis and function. Recent studies demonstrated the important function of IL-2 in preventing organ-specific inflammation independent of its role in Treg cells, via regulating the phenotype and function of the Th cells, which in-turn regulates the B-cell responses. The IL2−/− (IL2 knock-out (KO)) mice have much reduced Tregs that leads to spontaneous inflammation in pancreas, salivary glands, and liver (14-16). However, the Scurfy (Sf) mice, which are completely deficient in Tregs due to mutation in Foxp3 (the lineage regulator of Tregs), are resistant to inflammation in the pancreas, salivary glands, liver etc, although they develop multi-organ inflammation in the skin, lungs and stomach (14-16).
Deleting the IL-2 gene from the scurfy mice (the Sf.Il2−/− double mutant mice) induced pancreatitis, sialoadenitis, and hepato-cholangitis, suggesting that IL-2 suppresses inflammation in these organs independent of Tregs (14-16). However, deficiency of other suppressive cells (such as Th2) due to loss of IL-2 may further exacerbate the disease.
The involvement of the organs is reminiscent of an increasing number of patients who have autoimmune pancreatitis (AIP). These patients also have parallel or subsequent inflammation in salivary glands, hepato-biliary tree, and several other organs (Khosroshahi & Stone, A clinical overview of IgG4-related systemic disease Curr. Opin. Rheumatol., 2011, 23(1):57-66). The diseases has now been identified as a spectrum disorder, known as IgG4-related systemic disease (IgG4-RSD). These patients have elevated levels of IgG4 systemically as well as in the inflamed organs. The production of IgG4 during autoimmunity and IgE during allergic diseases is a result of increased TfH cell activity, which induces class-switching and somatic hypermutation in the B-cells. Our data implies that IL-2 is a negative regulator of several genes associated with the T-follicular helper cells (TfH), which are critical for the maturation of B-cells and for production of high-affinity antibodies (manuscript in preparation). Recent data from other groups also showed that IL-2 via STAT5 is a negative regulator of TfH cell differentiation (32, 33).
A strong correlation comes from Lupus patients, whose T-cells produce less IL-2, and show an increase in the TfH-mediated germinal center formation and increased production of autoantibodies (34). Data from T1D patients as well as non-obese diabetic (NOD) mouse models show strong correlations of hypomorphic variations in the IL-2 and IL-2 receptor (CD25) alleles (35). Similarly, in multiple sclerosis (MS), one of the strongest genetic correlations has been linked to the hypomorphic alleles of IL-2R (36, 37). The pro-inflammatory cytokine—IFN-γ produced by Th1 cells, is increased systemically as well as locally at the sites of inflammation in all these diseases.
Interestingly, a strong Th2 response was associated with lower incidence and well as resolution of T1D and MS in the human patients as well as mouse models (23-26). Treatment of mice with conditions that promote the Th2 immunity was found to be beneficial in several mouse models (23, 38-40).
IL-2 and Innate Lymphoid Cells (ILC):
A new subset of lymphocytes has been identified recently by several independent groups and has been named ILC, Nuocytes, and natural helper cells (9, 12, 13, 41). These cells do not express the characteristic cell surface markers of T- and B-lymphocytes and mainly reside at the mucosal surfaces and offer first line of defense against parasites. However, they express several cell surface molecules, such as CD90, c-Kit and IL-7Ra, indicative of their lymphoid origin. They also express high levels of CD25 (IL-2Ra) and T1/ST2 (IL-33R) (42-44). Stimulation of lung ILCs with IL-33 in combination with IL-2 and IL-7 resulted in production of IL-5 and IL-13, demonstrating that the ILC population in the lung resembles Type 2 ILCs that express Th2-associated cytokines (45, 46).
IL-33, ILC, and Th2 Cells:
IL-33 was discovered recently and is synthesized as a 270 amino acid protein that contains a nuclear localization signal (NLS) at the N-terminus and a C-terminal region with structural homology to IL-1 family cytokines (47-49). Full length IL-33 localizes to the nucleus where it associates with heterochromatin and mitotic chromosomes and may function as a transcriptional repressor (47-49). The intracellular apoptosis related protease Caspase-1 cleaves IL-33 to an 18 kDa C-terminal fragment, which has structure and functions similar to the IL-1 family cytokines. IL-33 expression was found upregulated in innate immune and epithelial cells in response to parasitic infections (50, 51).
The receptor for IL-33, IL1RL1 (also known as ST2), was identified long before the discovery of IL-33 and was considered an orphan receptor present on the surface of Th2 cells until the discovery of IL-33 (52, 53). IL-33 induces hetero-dimerization of IL1RL1 with IL-1RAcP, the co-receptor for IL-1 and IL-18. IL-33 is also considered an alarmin, which is released by cells undergoing apoptosis to induce clearance of the dying cells (52).
The ILC/Nuocytes, as well as Th2 cells, when stimulated with IL-33 upregulate the expression of IL-4, IL-5, and IL-13, the critical cytokines for the effector function of these cells against parasitic infections. Recent studies show that IL-33 promotes the function of ILC/Nuocytes as a first line of defense, before the adaptive immunity matures (12, 45, 54). Recent data also suggests that IL-33 production by the dendritic cells in response to allergens may be one of the mechanisms to initiate a Th2 response (55-57).
Anti-Inflammatory Role of IL-33:
Although, the primary function of IL-33 has been adjudged to boost the immunity against parasitic infections, recent data has identified several anti-inflammatory properties of IL-33. Several of these studies indicate a skewing towards the Th2-type of response, which results in resolution of the pro-inflammatory Th1 and Th17 responses (10, 58). Besides being chemo-attractive for and promoting the secretion of Th2 cytokines (IL-5 and IL-13) by the differentiated Th2 cells, IL-33 can prime murine dendritic cells to induce polarization of naïve T cells towards a Th2 phenotype (55-57). Further, IL-33 has been shown to enhance production of IgM antibodies and IL-5 and IL-13 production from B1 B-cells in vivo (59).
The natural IgM secreted by the B1 B-cells is widely accepted as anti-inflammatory under various settings (60, 61). In experimental asthma in the ovalbumin-induced airway inflammation model, the IL-33 receptor-deficient mice were not protected (62). Interestingly, in another model adoptive transfer of IL1RL1-deficient Th2 cells into immuno-deficient Rag1 KO mice induced greater disease than the IL1RL1-sufficient control mice (63).
Several inflammatory diseases are driven by IL-12 and IFN-γ-induced Th1 immune response and infiltration of immune cells in the target organs such as atherosclerosis. IL-33 treatment reduced the inflammation both in terms of lesion size as well as in terms of reduction in the infiltrating cells in mouse models of atherosclerosis (64, 65). This was accompanied with a switch in the cytokine profile from INF-γ to IL-4, IL-5, and IL-13 along with an increase in the levels of protective anti-oxidized low-density lipoprotein (ox-LDL) IgM antibodies. On the other hand, blocking the signaling with the use of soluble IL1RL1 (sST2) worsened the disease with high IFN-γ levels (66).
IL-33 has been shown to have important functions in the central nervous system (CNS), as indicated by strong expression of its mRNA in the brain and spinal cord and the levels are further increased under experimental inflammatory conditions (67, 68). The microglial and astrocytes also express the IL-33 receptor as detected by flow-cytometry (69). LPS stimulation of cultured microglia and astrocytes induced the expression of IL-33 in glial and astrocyte cultures. IL-33 treatment not only induced proliferation of microglial cells, but also induced the phagocytosis and secretion of IL-10, IL-10, and TNF-α by these cells (69). Finally, a transcriptional analysis of brain tissue from patients with Alzheimer's disease revealed that IL-33 expression was decreased compared to control tissues, suggesting that IL-33 may play an important neuroprotective role during infections and inflammatory conditions (70).
IL-33/IL1RL1 axis has recently been shown to be protective in type-2 diabetes (T2D). In vitro culture of adipocytes with IL-33 induced production of Th2 cytokines leading to reduced lipid storage and decreased expression of several adipogenesis related genes (71). In vivo, treatment of genetically obese diabetic mice (ob/ob) with IL-33 led to protective metabolic effects with reduced adiposity, reduced fasting glucose, and improved glucose and insulin tolerance. Conversely, mice lacking IL1RL1 were more susceptible to T2D upon high fat diet feeding as compared to the controls. The protection offered by IL-33 signaling was accompanied via switch in phenotype of macrophages from M1 (Th1 associated pro-inflammatory) to M2 (Th2 associated anti-inflammatory) (71). Recent studies have also shown that IL-33 can induce the Fat-associated lymphoid cells (FALC) to secrete IL-4, IL-5 and IL-13, which may be serve a protective role against inflammation during obesity (72).
There is a long felt need in the art for compositions and methods useful for treating autoimmune diseases and disorders and inflammation. The present application satisfies these needs.